High Efficiency Internal Combustion Stirling Engine Development

For the development of high efficiency and low emission combustion systems, high temperature air combustion technology has been tested by utilizing preheated air over 1100 K and exhaust gas recirculation. In this system, combustion air is diluted with large amount of recirculated exhaust gases, such that the oxygen concentration is relatively low in the reaction zone, leading to low flame temperature. Since, the temperature fluctuations and sound emissions form the flame are small and flame luminosity is low, the combustion mode is expected to be flameless or mild combustion. Experiment was performed to investigate the turbulent flame structure and NO^x emission characteristics in the high temperature air combustion focused on coflowing jet diffusion flames which has a fundamental structure of many practical combustion systems. The effect of turbulence has also been evaluated by installing perforated plate in the oxidizer inlet nozzle. LPG was used as a fuel. Results showed that even though NO^x emission is sensitive to the combustion air temperature, the present high temperature air combustion system produce low NO^x emission because it is operated in low oxygen concentration condition by the high exhaust gas recirculation.br/

<div class="section abstract"><div class="htmlview paragraph">The main objective of this work is to describe the design and testing of novel cam profiles, which are key for efficiency demonstration on a new class of internal combustion engine (ICE). A recuperated split cycle engine (RSCE) has unique demands for valve lift, duration and phasing when compared to a conventional 4-stroke. In particular, good control of the expander intake valve opening (IVO) appears to be necessary to achieve high efficiency.</div><div class="htmlview paragraph">Commercial computer programs available for valvetrains have been developed for conventional 4-stroke engines and, typically, these are focused on profile analysis rather than design. Often, the standards and recommended parameters are derived from historical 4-stroke data that may not fulfill the requirements of a new class of ICE, where boundary conditions have drastically changed.</div><div class="htmlview paragraph">In this paper, the cam profile requirements, functions, design, analysis and test results from a research and development (R&D) program of a heavy duty (HD) recuperated split cycle engine are reported. This included novelties in cam profile generation, technology and the materials used. This work is based on requirements, hypotheses and problem simplifications, supported by virtual validation, FEM analyses, spreadsheet calculations, component specifications and 1D simulations. Development has also been done by suppliers to satisfy the project requirements, alongside a compromise between technology selection and the pressing need to respect an extremely short time frame for component procurement.</div><div class="htmlview paragraph">Whilst this work refers to a specific engine development program, the methodology described in this paper has been more generally considered for the new class of ICE and can be successfully applied to other projects with common development targets (time to market, fuel efficiency and development costs).</div></div>

Gasoline compression ignition (GCI) using a single gasoline-type fuel for port fuel and direct injection has been shown as a method to achieve low-temperature combustion with low engine-out NOx and soot emissions and high indicated thermal efficiency. However, key technical barriers to achieving low temperature combustion on multi-cylinder engines include the air handling system (limited amount of exhaust gas recirculation (EGR)) as well as mechanical engine limitations (e.g. peak pressure rise rate). In light of these limitations, high temperature combustion with reduced amounts of EGR appears more practical. Furthermore, for high temperature GCI, an effective aftertreatment system allows high thermal efficiency with low tailpipe-out emissions. In this work, experimental testing was conducted on a 12.4 L multi-cylinder heavy-duty diesel engine operating with high temperature GCI combustion using EEE gasoline. Engine testing was conducted at an engine speed of 1038 rpm and brake mean effective pressure (BMEP) of 14 bar. Port fuel and direct injection strategies were utilized to increase the premixed combustion fraction. The impact on engine performance and emissions with respect to varying the injection and intake operating parameters was quantified within this study. A combined effect of reducing heat transfer and increasing exhaust loss resulted in a flat trend of brake thermal efficiency (BTE) when retarding direct injection timing, while increased port fuel mass improved BTE due to advanced combustion phasing and reduced heat transfer loss. Overall, varying intake valve close timing, EGR, intake pressure and temperature with the current pressure rise rate and soot emissions constraint was not effective in improving BTE, as the benefit of low heat transfer loss was always offset by increased exhaust loss.

High temperature air combustion provides the significant advantages of high thermal efficiency, reduced pollution, and low fuel consumption. The mathematical model for HTAC is built and the effect of oxygen concentration of entrancing chamber on combustion and NOx emission is investigated by using numerical simulation. In this paper, keeping the inleting oxygen concentration unchanged or unchanged have been made a comparative study. The results show that with the decrease of the entrancing chamber of oxygen concentration can effectively reduce the furnace temperature and make the furnace temperature more even uniform, and reduce the NO concentration.

In the present experiment, a computerized single cylinder diesel engine with a data acquisition system was used to study the effects of oxygen enriched combustion technology (OECT) on the performance characteristics. The use of different levels of oxygen-enriched air was compared with respect to percentage load. Increasing the oxygen content in the air leads to faster burn rates and increases the combustibility at the same stoichiometry (oxygen-to-fuel ratio). These effects have the potential to increase the thermal efficiency and specific power output of a diesel engine. The power increases considerably with oxygen enrichment. In addition, oxygen enrichment can also be considered as a way to reduce the sudden loss in power output when the engine operates in a high load condition. Assessed high combustion temperature from the oxygen enriched combustion leads to high combustion efficiency. OECT reduces the volume of flue gases and reduces the effects of greenhouse effects. Engine tests were conducted in the above said engine for different loads and the following performance characteristics like brake power (BP), specific fuel consumption (SFC), mean effective pressure, brake thermal efficiency, mechanical efficiency, and exhaust gas temperature were studied. The objective of this paper is to address, in a systematic way, the key technical issues associated with applying OECT to single cylinder diesel engines.

Experimental analysis and performance of refinery fuel gas on lean and rich fuel–air premixed combustion

Towards the development of an efficient low-NOx ammonia combustor for a micro gas turbine

The aim of this paper is to study the way of maximizing the thermal efficiency of gasoline engine. On the one hand, through the study of exergy loss in the combustion process, the thermodynamic parameters of low exergy loss in the combustion process were proposed, including low exergy loss equivalence ratio, low exergy loss initial combustion temperature, moderate EGR, high burst pressure, etc. On the other hand, the influence of engine thermodynamic cycle parameters on thermal efficiency, including engine compression ratio and specific heat ratio of charge, was studied. On the basis of the studies, the basic characteristics of high efficiency engine cycle, including lean burn, EGR, boosting and high compression ratio, were proposed. Then an experimental study on homogeneous compression combustion of gasoline with low exergy loss was carried out on a single cylinder engine. In order to suppress rough combustion, the equivalence ratio increases with the increase of load, and the boost pressure and combustion pressure must increase correspondingly. Appropriate increase of EGR can inhibit combustion rate, reduce heat loss and improve thermal efficiency. However, excessive EGR not only leads to the increase of incomplete combustion loss, but also reduces the thermal efficiency due to the decrease of specific heat ratio. What is interesting is that both the compression ratio and EGR can regulate the cycle temperature, but a change in the compression ratio does not change the specific heat ratio or the oxygen concentration. Therefore, thermodynamic parameters of low exergy loss and cycle parameters of high thermal efficiency are the approaches to achieve ultra-high thermal efficiency, whose limitation is the maximum burst pressure.KeywordsCI gasoline engineLean burn gasoline HCCILow exergy loss combustionThermodynamic cycle efficiency

This is the final report of the High Efficiency Clean Combustion (HECC) Research Program for the U.S. Department of Energy. Work under this co-funded program began in August 2005 and finished in July 2010. The objective of this program was to develop and demonstrate a low emission, high thermal efficiency engine system that met 2010 EPA heavy-duty on-highway truck emissions requirements (0.2g/bhp-hr NOx, 0.14g/bhp-hr HC and 0.01g/bhp-hr PM) with a thermal efficiency of 46%. To achieve this goal, development of diesel homogenous charge compression ignition (HCCI) combustion was the chosen approach. This report summarizes the development of diesel HCCI combustion and associated enabling technologies that occurred during the HECC program between August 2005 and July 2010. This program showed that although diesel HCCI with conventional US diesel fuel was not a feasible means to achieve the program objectives, the HCCI load range could be increased with a higher volatility, lower cetane number fuel, such as gasoline, if the combustion rate could be moderated to avoid excessive cylinder pressure rise rates. Given the potential efficiency and emissions benefits, continued research of combustion with low cetane number fuels and the effects of fuel distillation are recommended. The operation of diesel HCCI was only feasible at part-load due to a limited fuel injection window. A 4% fuel consumption benefit versus conventional, low-temperature combustion was realized over the achievable operating range. Several enabling technologies were developed under this program that also benefited non-HCCI combustion. The development of a 300MPa fuel injector enabled the development of extended lifted flame combustion. A design methodology for minimizing the heat transfer to jacket water, known as precision cooling, will benefit conventional combustion engines, as well as HCCI engines. An advanced combustion control system based on cylinder pressure measurements was developed. A Well-to-wheels analysis of the energy flows in a mobile vehicle system and a 2nd Law thermodynamic analysis of the engine system were also completed under this program.

High temperature alkali corrosion has been known to cause premature failure of ceramic components used in advanced high temperature coal combustion systems such as coal gasification and clean-up, coal fired gas turbines, and high efficiency heat engines. Non-oxide ceramics, such as SiC and Si{sub 3}N{sub 4}, are applied in HITAF systems for their well-known and desirable high temperature thermal and mechanical properties. However, these materials are prone to rapid corrosion under some types of high temperature coal combustion conditions. The objective of this research is to apply CMZP and Mg- Al{sub 2}TiO{sub 5} as coatings to SiC to improve corrosion resistance under coal combustion atmospheres as well as to improve high temperature mechanical properties. The research will not only develop and characterize CMZP and Mg-Al{sub 2}TiO{sub 5} coatings but will also strive to expand the existing knowledge of the mechanism of coal combustion corrosion of SiC in the temperature range of 1000- 4000{degrees}C.

Concerns related to global warming and environmental pollution concerns have pressured coal-fired power plants to improve efficiency and reduce emissions. However, the conventional efficiency improvement methods — increasing steam pressure and temperature and reducing condenser pressure are limited by material technology and the temperature of the available cooling medium. The next step for increasing efficiency would be to add additional reheat or regenerative cycles, but this is not feasible for existing plants. In addition, as the share of renewable energy and the grid’s demands on the coal-fired power plants increases, China’s coal-fired units are faced with more and tougher challenges, including large peak-valley gaps, frequent startups and shutdowns and cost pressures. As a result, the boiler combustion efficiency decreases and incidents such as furnace explosions, aggravation and collapsing of slag and burning of facilities located downstream of the economizer become more frequent. To address these problems, the generalized regeneration theory has been proposed and a series of related technologies have been developed, providing a new approach for not only improving the efficiency of coal-fired power plants, but also resulted in boiler operation that is cleaner and safer. These technologies which include anew boiler startup technology, the high efficiency combustion and low emission technology under low load and the low oxygen, and a low NOx and high efficiency combustion technology under high load have been implemented successfully in the Shanghai Waigaoqiao No. 3 power plant. By improving the utilization of turbine extraction and reducing the exhaust loss, these innovative technologies greatly improve the environmental performance, efficiency and safety of the units in various operating conditions. In addition, improvements have been made in the boilers ability to adapt to changing coal supplies, particularly for coal with high slagging tendencies and high moisture content.

The interactions between IC engine thermodynamics and knock

To date, 59 countries, representing 54% of global greenhouse gas emissions have made pledges for net-zero emissions targets within this century. This will require cleaner and more efficient sources of energy which is driving research into small-scale engines and auxiliary power units for hybrid vehicles and stationary power generation. A suitable candidate for such applications is the micro gas turbine due to its high-power density, reliability and low emissions. Further development of such engines is required though due to their increasing parasitic energy losses relative to net power output as size decreases. Additive manufacturing offers the design freedom to not only increase efficiencies but to also reduce emissions when applied to the various components of micro gas turbines. This article reports the effects of several additive manufacturing (AM) enabled design features for micro gas turbine combustion chambers via experimental testing of full-scale parts. The main objective of the additively manufactured features is the reduction of exhaust emissions by improving the air-fuel mixture distribution and consequently ignition and combustion. Using additive manufacturing a novel conical radial swirl-stabilized tubular combustor with internal vane fuel injection was created as a baseline for the laboratory testing. Several other features, including augmented backside liner cooling surfaces, in-vane lattice structures for fuel mixing and upstream liner fuel injection rings were also generated to further the investigations into additively manufactured features and their effects on fuel mixing. Using multiple combinations of all these features, 10 geometries were generated and tested at a variety of operating conditions. Three inlet temperatures were tested (500°C, 600°C and 700°C) with varying fuel flow rates to investigate their operating limits at a constant inlet pressure of 4 bar absolute. Test results for the full range of equivalence ratios and operating conditions showed that the upstream liner fuel injection designs generated NOx, CO and THC emissions on par with the baseline but showed a reduction in the maximum and minimum operating ranges. This design, however, demonstrated the distinct advantage of being able to ignite at full air mass flow; this is not possible with the baseline designs and is also an added benefit to its main use which is the reduction of liner temperature. Overall, the test results underscore that designing combustion chambers for additive manufacturing can provide a myriad of benefits not only for micro gas turbines but also for other applications requiring high efficiency combustion chambers.

A study was made to evaluate the potential of a Stirling engine for significant improvement in emissions and fuel economy over the present-day internal combustion engine and to initiate, on the basis of the experience gained in the Ford/Philips 170 hp Stirling engine development program, the design of an engine in the 80 to 100 hp range suitable for use in a passenger car in the 2,500 to 3,000 lb weight class. The final report given covers two major tasks. Task I was the Contractor-financed testing of a 170 hp Stirling engine powered Torino passenger vehicle. The fuel economy of the 170 hp Stirling engine-powered Torino approximates that of similar 1977 model year production passenger vehicles in a comparable weight class, with comparable performance. Emissions meet the objective of 0.41/3.4/0.4 grams per mile (HC/CO/NO/sub x/). Task II was a design study of an 80 to 100 hp engine in a passenger car in the 2,500 to 3000 lb weight class based on the 170 hp Torino installation. The baseline vehicle selected for comparison purposes is a 1976 Pinto with a 2.3 liter 4-cylinder engine. The engine is rated 84 hp, with 4 double-acting cylinders, each of 98 cc displacement (4 to 98), and utilizes a swashplate drive. The swashplate Stirling engines did not package well in the compact car. Despite optimization of the engine to achieve minimum length, the Stirling powered compact car was 89 mm (3.5 inches) longer than its Pinto baseline. Fuel economy of the swashplate engine was adversely affected by attempts to fit it within the Pinto engine compartment. The 4 cylinder-dual crankshaft Stirling engine resulted in a very attractive vehicle. The engine packaged within the confines of the Pinto engine compartment. However, the packageable engine did not incorporate the rotary preheater as used on the swashplate engine. Emissions and noise level objectives could be met.

Pacific Northwest Laboratory (PNL) reviewed research projects that are related to the development of Stirling engines and that are under way at Japanese national laboratories and universities. The research and development focused on component rather than on whole engine development. PNL obtained the information from a literature review and interviews conducted at the laboratories and universities. The universities have less equipment available and operate with smaller staffs for research than do the laboratories. In particular, the Mechanical Engineering Laboratory and the Aerospace Laboratory conduct high-quality component and fundamental work. Despite having less equipment, some of the researchers at the universities conduct high-quality fundamental research. As is typical in Japan, several of the university professors are very active in consulting and advisory capacities to companies engaged in Stirling engine development, and also with government and association advisory and technical committees. Contacts with these professors and selective examination of their research are good ways to keep abreast of Japanese Stirling developments.